While my guess would have been A as well, there are many possible reasons and i find it interesting most who guessed a reason laid it on the wives &/or children tho unless there was a huge blow up between wives would not have to end the carpooling of the husband.
Other possible reasons:
1) If the men made this arrangement without consulting both wives, that could be problematic in itself.
2) The logistics of when/how the babysat child got dropped off at the care giving Wife's house might have inconvenienced one or both wives. But that would be on their spouses for not consulting them.
As likely,
3) I have found that many men, especially if older than Gen X struggle with being a passenger in a car. Not being in control is one issue, deciding who drives what day another, and what each thinks of other's driving a third.
4) Not negotiating details like who's car is used, if alternating, and the financial details they didn't share (perhaps because they had not gotten them worked out in detail?) are possible deal breakers. Was the child care negotiated as part of their financial arrangement if the car of the one whose child was being cared for was used all the time? Again while that means one or both wives may have wanted the arrangement ended, the responsibility for its failure would be on the men if the wives hadn't had any say in making the arrangements.
5) Their morning &/or afternoon commute modes may have been very different--one preferring quiet or small talk the other a talker, or like me--perceived as unreasonably cheerful in the morning even if not talking much, coversation may have revealed political differences when they had extended non-work hours together in a car.
6) Various combinations of 1-5.
It us rarely as simple as it seems to those not directly involved and dometimes even the parties to such arrangements might have trouble defining the dealbreaker(s) unless their defaukt mide us to blame everyone but themselves when they didn't think it through and lay out terms properly.
